Just as solar leasing from the likes of SolarCity unlocked the solar market in the U.S., pay as you go solar providers are unlocking solar power for the masses worldwide.

That's a big reason the off-grid solar market is booming, with over $45 million flowing into the market since November 2013 and a smorgasbord of start-up companies popping up for investors to choose from. Recently, the National Geographic's Terra Watt Prize validated this market trend by awarding two 'pay-as-you-go' off-grid solar companies its top honors.

Focused on rural village electrification, the Terra Watt Prize was created to provide entrepreneurs with access to investment and the opportunity to be reviewed by credible experts which in turn provides valuable business exposure.

This year's winners -- who were evaluated on feasibility, impact, sustainability, and scalability of their products -- are India-based Mera Gao Power and Tanzania-based EGG-energy. Each company will receive $125,000, plus the prestige of being honored by National Geographic through a rigorous process designed to add to the due diligence process.

Mera Gao Power produces and operates micro grids in rural Uttar Pradesh, one of India's poorest states but also a hotbed of distributed solar activity. The company describes itself as a 'lighting utility' and lights its customers lives with highly efficient LED bulbs. Mera Gao Power collects weekly payments, and if those payments aren't received, the micro grid systems shut themselves off via self-resetting fuses. This unique model has allowed the young company to expand power to more than 100,000 people.

EGG-energy has been working toward their mission of scaling up the solar home system (SHS) distribution in Tanzania and East Africa. EGG-energy started in 2009 as an on-grid battery business (the "Netflix of batteries"), then expanded their battery business to include off-grid areas, and eventually added SHS to their portfolio. Today, EGG-energy is focused on expanding their 'rent to own' 80 and 200-watt SHS across Tanzania and East Africa by using mobile money platforms that allow them to remotely monitor their systems.

As we've pointed out before, mobile phone penetration and off-grid solar are converging to create clean technology's next big market. It is one of the most innovative and exciting opportunities the international community has seen in a long time. But for too long it has gone unnoticed as a silent revolution in rural parts of the developing world.